Method of improving the adhesion of nylon to rubber



Patented June 11, 1946 METHOD OF IMPROVING THE ADHESION OF NYLON TO RUBBER Jack Compton, Cuyahoga Falls, Ohio, assignor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York No Drawing. Application April 26, 1943, Serial No. 484,600

Claims.

This invention relates to a method of improving the adhesion of fibrous structures such as yarns, cords and fabric comprising nylon fibers and filaments, i. e., fibers and filaments of synthetic linear polyamides, to a rubber material, and to the resulting composite product comprising such fibrous structures and a rubber material in adhering relation.

Fibrous structures comprising nylon are Well known to possess many properties such as high tensile strength, elasticity and resistance to flexing, which render them particularly useful as reinforcing elements for rubber materials as in the manufacture of pneumatic tires, belts and the like. Nylon has the disadvantage, however, of possessing relatively poor adhesion to rubber, only a fraction of that of cotton, and consequently rubber structures comprising nylon filaments tend to pull apart in service.

I have now discovered a method of treating fibrous structures comprising nylon, whether in the form of yarns, cords, fabric or the like, preparatory to their incorporation in a body of a rubber material and vulcanization of the composite product, whereby the adhesion of the nylon to the rubber material in the final vulcam'zed product is remarkably increased. This method comprises first treating the fibrous structure with a solvent which is capable of dissolving nylon, preferably a solvent containing dissolved nylon; then, immediately after such treatment, further treating the fibrous structure with a material which dissolves the nylon solvent but does not dissolve nylon. After drying the fibrous structure so treated it is found to possess a roughened surface and to adhere well to rubber materials when incorporated therein.

Before describing the invention in detail the nature of the fibrous structures treated will be more particularly set forth. As mentioned above the fibrous structures employed are those comprising fibers or filaments of synthetic linear polyamides. Fiber-forming synthetic linear polyamides or superpolyamides and filaments produced therefrom are well known to the art by the ge ric name of nylon and are described in U. Patents Nos. 2,071,250, 2,071,253 and 2,130,943. These synthetic linear polyamides are of two types, those derived from polymerizable monoaminomonocarboxylic acids or their amideforming derivatives and those obtained by the condensation polymerization of diamines with dibasic carboxylic acids or their equivalents. The most widely used synthetic linear polyamide is polyhexamethylene adipamide which is prepared by the condensation polymerization of hexamethylene diamine with adipic acid. Yarns, cords and fabric prepared from this and other synthetic linear polyamides and designed especially for reinforcing rubber structures are more fully described in U. S. Patent 2,273,200, and are preferred fibrous structures for use in this invention. Such yarns and cords are prepared from synthetic linear polyamide filaments which have been oriented by cold drawing and which possess an elongation of about 15 to All such fibrous structures are herein sometimes referred to for sake of brevity as fibrous structures comprising nylon, it being understood that this expression includes yarns, cords and fabrics prepared wholly from fibers or filaments of synthetic linear polyamides or partly from such fibers or filaments and partly from other textile fibers such as cotton and rayon.

In the practice of the invention such fibrous structures comprising nylon are first treated with a nylon solvent, preferably a nylon solvent containing from 1 to 20% of dissolved nylon, i. e., of a dissolved synthetic linear polyamide. Solvents in which nylon is soluble includes phenols, or aromatic hydroxy compoundsfsuch as phenol itself, cresol, resorcinol, phloroglucinol, hydroquinone or the like, which are the preferred nylon solvents, and other nylon solvents such as formic acid and ethyl alcohol as well as mixtures of such solvents with ketones, such as acetone, aliphatic alcohols such as ethyl alcohol and the like. Treatment of the fibrous structure with the nylon solvent or nylon solution is preferably accomplished by dipping the fibrous structure in the solvent or solution although other methods I of treatment such as by spraying may also be employed. The treatment is continued for a time suficient only to produce a surface layer of a nylon solution on the fibrous structure and is terminated before the tenacity of the fibers or filament is reduced to a harmful degree, this being done usually by treatments of from about 1 second to 3 minutes depending on the solvent and the concentration of dissolved nylon in the solvent if any.

' 3 water while nylon itself is water insoluble. Other liquids which may similarly be employed include, however, alcohols such as methanol, ethanol, propanols etc. or mixtures thereof with 'water as well as any other liquid material in which the nylon solvent is soluble and the nylon insoluble or difllcultly soluble. Since the fibrous structures are dried after treatment with the liquid material, a material which is volatile at temperatures below about 150 C. is preferred.

This treatment with the liquid material in which the nylon solvent is soluble is also preferably carried out by dipping the fibrous structure in the liquid material. The duration of this latter treatment is not critical and is preferably continued for a time sufficient to remove substantially all of the nylon solvent from the surfaces of the fibrous structure.

After the successive treatments with nylon solvent or solution and with a liquid which dissolves the solvent but does not dissolve nylon, the fibrous structure comprising nylon is then dried in air or in a heated chamber preferably under a tension suiiicient to maintain the fibrous structure in its original dimensions. The treated fibrous structure is then incorporated in a body of an unvulcanized but vulcanizable composition comprising a rubber material in the manner well known to the art for incorporatin fibrous structures into rubber composition in making tires, belts and the like, and the resulting rubber-fiber composite structure is vulcanized. It has been found that by the method of this invention it is possible to produce an adhesion between the nylon fibers and the rubber over 600% greater than that obtained when untreated nylon fibrous structures are incorporated in rubber compositions.

In a representative embodiment of the invention a nylon cord, composed of oriented polyhexamethylene adipamide fibers, is dipped for five seconds in a 50% resorcinol 50% ethyl alcohol solution containing of dissolved polyhexamethylene adipamide, and is then immediately immersed into water for 30 seconds. The cord is then removed from the water and is dried under sufiicient tension to maintain it in its original length. It is then incorporated into a natural rubber composition and the composition vulcanized. Upon testing the adhesion of the nylon cord to the rubber, and comparing the adhesion thus obtained with the adhesion of a similar untreated nylon cord incorporated in a similar rubber composition, it is found that a 615% increase in adhesion is obtained.

The terms a rubber material and a rubber composition as used herein are meant to include not only natural rubber but also elastic vulcanizable synthetic rubbers such a copolymers of butadiene-1,3 with styrene, acrylonitrile,

isobutylene and the like, polymers of 2-chloro' butadiene-1,3 and other synthetic rubbers whether or not admixed with conventional vulcanizing and compoundin ingredients.

As many widely different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention i not to be limited to the specific embodiments thereof except as set forth in the appended claims.

I claim:

1. In a. method of making a composite product by incorporating a fibrous structure comprising fibers of a synthetic linear polyamide in a vulcanizable'rubber material and then vulcanizing the rubber material, the additional steps which comprise immersing the fibrous structure in a solution of a synthetic linear polyamide in a solvent therefor, removing the fibrous structure from the solution before the tenacity of the fibers has been substantially reduced, immediately reimmersing the fibrous structure in a composition consisting exclusively of liquid material in which said solvent-is soluble and in which the said synthetic linear polyamide is insoluble, removing the fibrous structure from the liquid material and drying the fibrous structure before incorporating the fibrous structure in a rubber material.

2. In a method of making a composite product by incorporating cords comprising oriented fibers of a synthetic linear polyamide in a vulcanizable rubber material and then vulcanizing the rubber material, the additional steps which comprise treating the cords with a solution containing from 1 to 20% of a synthetic linear polyamide dissolved in a solvent therefor to produce a coating of the said solution on the surfaces of said cords, immediately again treating the said cords with a composition consisting exclusively of liquid material in which the said solvent is insoluble and in which the said synthetic linear polyamide is insoluble to remove the said solvent from the surfaces of said cords and drying the treated cords up .er tension before incorporating the cords in the rubber material.

3. In a, method of making a composite product by incorporating a fibrous structure comprising oriented fibers of a synthetic linear polyamide in a vulcanizable rubber material and then vulcanizing the rubber material, the additional steps which comprise treating the said fibrous structure with a, solution of a synthetic linear polyamide in. a water-soluble phenolic solvent therefor to produce a coating of the said solution on the surfaces of the fibrous structure, immediately again treating the said fibrous structure with clear water to remove the water-soluble phenolic solvent from the surfaces of said fibrous structure and drying the so treated fibrous structure under tension before incorporating the fibrous structure in a rubber material.

4. The method of claim 3 wherein the synthetic linear polyamide is polyhexamethylene adipamide.

5. In a method of making a composite product by incorporating cords comprising oriented fibers of a synthetic linear polyamide in a vulcanizable rubber material and then vulcanizing the rubber material, the additional steps which comprise immersing the cords in a solution containing from 1 to 20% of a synthetic linear polyamide dissolved in resorcinol, removing the cords from the solution before the tenacity of the fibers therein hasbeen substantially reduced, immediately reimmersing the cords in clear water, removing the cords from the water and drying the cords under tension, all before incorporating the cords in the rubber material.

JACK COMPTON. 

